Name: thevenin circuit equivalents
Uploaded: 2024-04-11T12:48:31.000Z
Duration: 1 min 15 s
Channel: JoVE

Il teorema di Thevenin afferma che qualsiasi circuito lineare a due terminali può essere sostituito da un circuito equivalente con una singola sorgente di tensione in serie con un resistore.
In assenza di carico, la tensione attraverso i terminali aperti sarà la tensione di Thévenin.
Per trovare la resistenza al Thévenin, tutte le fonti indipendenti vengono disattivate. Quindi la resistenza vista attraverso i terminali è la resistenza di Thévenin.
Se il circuito contiene sorgenti dipendenti, le sorgenti indipendenti vengono comunque disattivate, ma ai terminali viene applicata una sorgente di test nota.
Dalla tensione o corrente terminale risultante, è possibile determinare la resistenza di Thévenin.
Infine, il carico viene collegato al circuito equivalente. La corrente attraverso il carico viene calcolata utilizzando la formula del divisore di corrente. Utilizzando la legge di Ohm, viene determinata la tensione di Thévenin attraverso il carico.
Una batteria può essere rappresentata come il circuito equivalente di Thévenin. La tensione di thévenin è la tensione a circuito aperto della batteria e la resistenza è la sua resistenza interna.
Conoscendo i parametri di Thévenin, è facile calcolare la corrente per vari carichi senza riesaminare l'intero circuito.

il teorema di thevinin

Il teorema di Thévenin gioca un ruolo fondamentale nell'analisi dei circuiti elettrici, offrendo una soluzione alle sfide poste dai carichi variabili all'interno di un circuito. Nelle applicazioni pratiche, è comune incontrare circuiti in cui alcuni elementi rimangono fissi mentre altri fluttuano, spesso definiti "carico". Una tipica presa elettrica domestica costituisce un ottimo esempio di carico variabile, poiché può essere collegata a una varietà di apparecchi, ciascuno con le proprie caratteristiche elettriche uniche. Ogni volta che un nuovo apparecchio viene collegato o rimosso, l'intero circuito richiede una nuova analisi. Il teorema di Thévenin fornisce una tecnica che sostituisce la porzione fissa del circuito con un circuito equivalente, semplificando così l'analisi e la progettazione.

Il teorema di Thévenin afferma che un circuito lineare a due terminali può essere rappresentato da un circuito equivalente costituito da una sorgente di tensione in serie con un resistore. Questo circuito equivalente incapsula efficacemente il comportamento del circuito originale da una prospettiva esterna. Due parametri critici definiscono questo circuito equivalente di Thévenin: la tensione equivalente di Thévenin (VTh), che corrisponde alla tensione a circuito aperto ai terminali, e la resistenza equivalente di Thévenin (RTh), che rappresenta l'ingresso o la resistenza equivalente ai terminali quando tutti le fonti indipendenti sono disattivate.

Per illustrare ulteriormente il concetto, si considerino due circuiti mostrati nella Figure 1 e nella Figure 2. Questi circuiti sono considerati equivalenti quando condividono la stessa relazione tensione-corrente ai loro terminali. Quando i terminali vengono lasciati a circuito aperto, con conseguente assenza di flusso di corrente, la tensione attraverso i terminali aperti sarà la tensione di Thévenin. Quando tutte le fonti indipendenti sono disattivate. Quindi la resistenza vista attraverso i terminali è la resistenza di Thévenin.

<img alt="Figure1" src="/files/ftp_upload/15053/15053_PT_Figure_1.svg" style="text-align: center; height: 128px;">
Figure 1
<img alt="Equation1" src="/files/ftp_upload/15053/15053_PT_Equation_1.svg" style="text-align: center; height: 14px;">

<img alt="Figure2" src="/files/ftp_upload/15053/15053_PT_Figure_2.svg" style="text-align: center; height: 128px;">
Figure 2
<img alt="Equation2" src="/files/ftp_upload/15053/15053_PT_Equation_2.svg" style="text-align: center; height: 14px;">

Per applicare praticamente questa idea e determinare la resistenza di Thévenin, dobbiamo considerare due scenari:

CASO 1: Nelle situazioni in cui la rete non contiene sorgenti dipendenti, tutte le sorgenti indipendenti vengono disattivate e viene accertata la resistenza di ingresso, che è la resistenza vista tra i terminali a e b.

CASO 2: Quando la rete incorpora fonti dipendenti, continuare a disattivare tutte le fonti indipendenti. Evitare tuttavia di disattivare le sorgenti dipendenti poiché sono controllate dalle variabili del circuito.

Vale la pena notare che il valore della resistenza di Thévenin (RTh) può talvolta essere negativo, a indicare che il circuito fornisce energia anziché consumarla. Questo scenario è fattibile in circuiti con sorgenti dipendenti.

Il teorema di Thevinin

Il teorema di Thevenin afferma che qualsiasi circuito lineare a due terminali può essere sostituito da un circuito equivalente con una singola sorgente di tensione in serie con un ...

Education

Didattica

JoVE Core

Electrical Engineering

Ingegneria elettrica

Unit 1

Unità 1

DC Circuit Analysis

Analisi dei circuiti in CC

KEY TERMS AND CONCEPTS

TERMINI E CONCETTI CHIAVE

Thevinin's Theorem

thevenin circuit equivalents

Thevenin circuit equivalents simplify linear two-terminal circuits by replacing the fixed part of a network with one equivalent source and one resistor. This method is useful when a circuit has a fixed section and a load that can change. A household electrical outlet is a familiar example, because different appliances can be plugged in or removed. Each change in load can require a new circuit analysis, so an equivalent circuit makes the work easier.

Thevenin's theorem states that a linear two-terminal circuit can be represented by a voltage source in series with a resistor. From the outside, this equivalent circuit has the same behavior as the original network. Two circuits are considered equivalent when they have the same voltage-current relationship at their terminals. The Thevenin equivalent voltage, VTh, is the open-circuit voltage at the terminals, and the Thevenin equivalent resistance, RTh, is the input resistance seen at the terminals when the independent sources are turned off.

To find the Thevenin resistance, the method depends on the kind of sources in the network. If the circuit has no dependent sources, all independent sources are deactivated and the resistance between terminals a and b is found. If the network includes dependent sources, the independent sources are still turned off, but the dependent sources stay active because they are controlled by circuit variables. In some cases, RTh can be negative. That means the circuit is supplying power instead of consuming it, which can happen in circuits with dependent sources.

Thevenin Circuit Equivalents

nodal analysis

Using Node Voltages in Circuit Analysis

Nodal analysis uses node voltages to simplify circuit analysis. In this method, the voltage at each node becomes the main variable. Once those voltages are known, they can be used to find other values, such as the current through specific circuit parts. The process begins by choosing a reference node, also called a datum node. This node is selected for convenience and assigned a voltage of zero. The other nodes, called non-reference nodes, are then measured relative to that point. In the...

nodal analysis with voltage sources

Supernode Equations in Nodal Analysis

Nodal analysis uses node voltages and Kirchhoff’s laws to solve circuits with voltage sources. It is a systematic method for breaking a complex circuit into smaller parts that are easier to analyze. In this example, the circuit includes four resistors and two voltage sources. One voltage source is connected between a non-reference node and the reference node. In that case, the non-reference node voltage can be written directly as the source voltage. This removes one unknown and makes the...

mesh analysis

Mesh Currents for Circuit Analysis

Mesh currents give students a simpler way to analyze planar circuits. In mesh analysis, the unknowns are currents, not voltages. The method uses Kirchhoff's voltage law, or KVL, to build the equations needed to solve the circuit. A mesh is a closed loop in a circuit that does not contain any smaller loops inside it. Each independent mesh is assigned a mesh current, and this current is usually drawn in the clockwise direction. These mesh currents are used as the main circuit variables during...

mesh analysis with current sources

Current Sources in Mesh Circuit Analysis

Current sources make mesh circuit analysis easier because they can reduce the number of equations needed. This applies to both independent and dependent current sources. The method depends on where the current source is placed in the circuit. When a current source appears in only one mesh, the setup is simple. Assign mesh currents as usual, but leave out the mesh that contains the current source from the equation process. Then apply Kirchhoff's voltage law, or KVL, to the remaining mesh to get...

source transformation

Circuit Source Equivalents

Circuit source equivalents make it easier to simplify electrical circuits in circuit analysis. A source transformation replaces a voltage source in series with a resistor by a current source in parallel with a resistor, or it replaces a current source in parallel with a resistor by a voltage source in series with a resistor. The key idea is that the equivalent resistance at the circuit terminals stays the same when the original sources are turned off. When making the change, the current source...

linear circuits

Circuit Linearity and Resistor Behavior

Circuit linearity describes how a circuit responds when its input changes. A linear circuit has an output that is directly proportional to its input. This behavior follows two rules: homogeneity and additivity. Homogeneity means that if the input, or excitation, is multiplied by a constant factor, the response is multiplied by the same factor. For example, if the current is increased by a constant k, the voltage also increases by k times. Additivity means that the response to a sum of inputs...

superposition theorem

Analyzing Circuits with Superposition

Superposition is a circuit analysis method for linear circuits with more than one independent source. It lets you find the voltage across or current through an element by adding the separate effects of each source acting alone. To use superposition, keep one independent source active and turn off the others. A voltage source is replaced by a short circuit, and a current source is replaced by an open circuit. Then calculate the output from the single active source. Repeat the process for each...

thevinin's theorem

Thevenin circuit equivalents simplify linear two-terminal circuits by replacing the fixed part of a network with one equivalent source and one resistor. This method is useful when a circuit has a fixed section and a load that can change. A household electrical outlet is a familiar example, because different appliances can be plugged in or removed. Each change in load can require a new circuit analysis, so an equivalent circuit makes the work easier. Thevenin's theorem states that a linear...

norton's theorem

Norton Equivalent Circuit in DC Analysis

Norton equivalent circuit in DC analysis shows how a linear two-terminal circuit can be replaced by a simpler network. The replacement uses a current source, called I_N, in parallel with a resistor, called R_N. I_N is the short-circuit current through the terminals, and R_N is the input or equivalent resistance seen at the terminals when the independent sources are turned off. To find Norton's resistance, all independent sources in the circuit are set to zero. The resistance measured at the...

maximum power transfer

Load Matching in Thevenin Circuits

Load matching in Thevenin circuits helps a source deliver the most power to a connected load. This matters in engineering fields such as telecommunications, where power delivery must be optimized. Even then, internal losses can be significant and may equal or exceed the power sent to the load. The Thevenin equivalent circuit is a useful way to study this situation. It replaces the full linear circuit with a simpler source and resistance while keeping the load in place. In this setup, the load...

design example: strain gauge bridge or wheatstone bridge

design-example-strain-gauge-bridge-or-wheatstone-bridge

Wheatstone Bridge Output for Strain Gauge Design

A strain gauge and Wheatstone bridge work together to turn mechanical strain into an electrical signal. In engineering, this setup is often used to measure force or pressure. Each part of the bridge has a resistance that changes slightly when strain is applied. The main goal is to turn a very small voltage output into a larger, easier-to-read signal. A voltmeter can then measure that output more clearly. To do this, an engineer designs the strain gauge circuit and figures out how much...

key terms and concepts

Learn how Thevenin’s theorem replaces a linear two-terminal circuit with a voltage source and resistor, and how to find VTh and RTh in circuit analysis.

Thevenin Circuit Equivalents | JoVE K12

JoVE Core Electrical Engineering offers easy-to-understand animated videos that cover fundamental concepts of electric circuits along with circuit analysis techniques. It incorporates first-order and second-order circuits using operational amplifiers and circuit transformation concepts. The inclusion of practical design examples and real-world applications through scientist-in-action videos adds significant educational value, making complex concepts accessible.

electrical engineering

Thevenin Circuit Equivalents

Description

Transcript

Tags